Modular Design And Hydrodynamic Study Of A Large Floating Foundation Based On Bi-hexagonal Structure

Nowadays,coastal countries are interested in offshore renewable energy.The development and utilization of renewable energy technologies,such as wind,solar and wave power,have made significant breakthroughs,providing an important solution for realizing low-carbon energy utilization.Going deep sea is one of the effective ways to reduce comprehensive costs.At present,problems such as high manufacturing costs,long construction period and single energy type are widespread,which limit the large-scale application of offshore new energy.In order to solve the above problems,this thesis proposes a large floating foundation configuration of bi-hexagon structure that can be assembled on site.The mechanical characteristics was systematically studied,in order to provide a new solution for the design and manufacture of large-scale floating bodies.The problems in the design and manufacture of large floating foundations were analyzed,and a new floating foundation with bi-hexagon structure was proposed,in which the sphere-bar node was used as the basic buoyancy element.By analyzing the topological configurations and mechanical characteristics of the basic element,the "five bar + single spherical joint" configuration was determined,and the reasonable direction of the force on the element structure was studied.Based on the advantages of bi-hexagon structure,the configuration method of large floating foundation with bi-hexagon structure was discussed.An assembly method on site of large-scale floating foundation with bihexagon structure was proposed.The static characteristics of the floating foundation with bi-hexagon grid structures(BHGS)were studied.The BHGS is equivalent to space grid structures of bi-hexagon structure.The linear and nonlinear mechanical behaviors of different types of doublelayer grid structures were compared by the finite element method.The linear and nonlinear mechanical behaviors of octahedron and double honeycomb multilayer grid structures were also studied.The results show that the BHGS significantly reduces the complexity of the node,improves the overall stress distribution,saves materials,and is conducive to node manufacturing and on-site assembly manufacturing.In addition,through the random design and first-order optimization method,the key dimensions of the floating foundation with BHGS were designed and optimized.According to the optimized floating body dimensions,the multi-purpose bi-hexagon floating foundation system was designed,along with the overall parameters of the system.The stability of the floating foundation with large inclination angle was studied,and two schemes of single point mooring and multi-point mooring were designed for different application scenarios.The wave parameters and characteristics for the interaction study of floating bodies with the bi-hexagon floating foundation(BHFF)were studied.Based on the wave data of the South China Sea for many years and the size characteristics of the floating body with double honeycomb structure,15 groups of wave combinations suitable for numerical analysis and experimental verification were selected.The kinematic characteristics of fifteen groups of waves were studied by using wave theory.The results show that the waves span from linear waves to second-order,third-order and fourth-order Stokes waves.The wave with the highest frequency is fourth-order Stokes waves.All waves do not meet the wave breaking conditions,ensuring the integrity of the waves.The random wave parameters of JONSWAP and P-M spectrum are studied,and the JONSWAP random wave parameters are given based on the floating body size.For the numerical calculation of floating foundation,the hydrodynamic model and motion response model of floating body were established based on potential flow theory.In the hydrodynamic model,the boundary element method and 3D panel method were used to discretize the control equations of the BHFF,which realizes the efficient calculation of the velocity potential.The key degrees of freedom were decoupled by using the dual symmetry of the BHFF.By calculating the additional mass and inertia moment corresponding to the natural period of DOFs,and combining the hydrostatic stiffness and mooring stiffness,the viscous damping was modified in the motion response model.And the motion parameters of the floating foundation and the wave action were solved.The effects of wave incidence azimuth and frequency on the BHFF response were studied,and cross validation was conducted by near-field method and far-field method.The results show that the response of the floating body is the largest under the action of head waves,and the mooring types has little influence on the translation and roll of the floating foundation.The pitch motion of single point mooring is larger than that of multi-point mooring,and the overall amplitude response is within a small range.In order to better verify the accuracy of the numerical model and the performance advantages of the BHFF,two prototypes were developed.The hydrostatic oscillation tests under different mooring modes and the dynamic response of the floating body under the action of regular and random waves were completed.The classic SPAR was introduced for comparative analysis.The results show that compared with the traditional SPAR,the BHFF has good hydrodynamic performance in the whole wave frequency range,and the overall performance of multi-point mooring is better than that of single point mooring,which is reflected in smaller mooring force and motion response.Considering the wind load and increasing the upper layer load,the response of the BHFF fluctuates less,and the experimental results are in good agreement with the numerical simulation.